Test unit for use at a network interface device

ABSTRACT

A test unit provides testing capability at a network interface device (NID). The test unit may be remotely activated so that testing is initiated upon activation from a remote site. In one embodiment, a characteristic signal is sent over a telephone line toward the NID. A characteristic signal is detected and the testing unit is activated. The testing unit may perform multiple types of tests, including tests for detecting line loss, line noise and latency. The test may be implemented using electronic circuitry or using an intelligent computer system.

TECHNICAL FIELD

The present invention relates generally to telecommunication systems andmore particularly to a test unit for use at a network interface device,including long distance lines, local lines and subscriber equipment.

BACKGROUND OF THE INVENTION

The United States Public Switched Telephone Network (PSTN) includes anumber of different components. Each of these components was originallyunder the ownership and control of a single telephone service provider.Currently, however, respective components in the PSTN may be ownedand/or under the responsibility of different parties. For example, along distance telephone company may be responsible for long distancelines, whereas a local telephone company may be responsible for locallines, and a subscriber may be responsible for equipment at thesubscriber premises.

When a malfunction in the PSTN arises, it is necessary to identifywhether the malfunction is due to a problem located at the subscriberpremises, in the subscriber loop or in the network of a chosen serviceprovider. Responsibility for correcting the problem lies with the partyresponsible for the component where the problem lies. Matters arecomplicated by multiple service providers competing for local telephonecommunication services. As a result, the subscriber loop may be ownedand maintained by one company yet leased by another company thatprovides local services to subscribers. Hence, each local serviceprovider needs a way to immediately test for proper functioning of thenetwork as far as a network interface device (NID). The NID ispositioned at the DEMARC, i.e., the demarcation point where a localtelephone company responsibility stops and the subscriber responsibilitybegins. Typically, the NID is located either adjacent to a subscriber'spremises or a short distance away from the subscriber's premises. Thus,there is a need to be able to determine the location of a problem withinthe PSTN without incurring significant overhead and without sufferingsubstantial delay.

SUMMARY OF THE INVENTION

The present invention addresses limitations of the conventional systemby providing a remotely activated test unit at a NID. The test unit canperform a number of different tests to identify malfunctions and todetermine the location of problems. For example, the test unit may beable to generate tones, silence a line and identify latency fortransmitted signals. The test unit may be remotely activated toeliminate the need for sending maintenance personnel out to the NID.

In accordance with one aspect of the present invention, a component fortesting a portion of a network is provided in a NID. The componentincludes a testing module for performing testing on a portion of thenetwork as well as an activation module for activating the testingmodule to perform the testing. The activation module includes a remoteactivator for remote activation. The remote activator may take the formof a tone detector for detecting a characteristic tone or a radiofrequency detector for detecting at least one characteristic radiosignal for activating the testing module. The testing module includes atone generator for generating a test tone. In addition, the testingmodule includes a silencing element for silencing a portion of thenetwork or a loop-back element for echoing signals over a portion of thenetwork.

In accordance with a further aspect of the present invention, a systemis provided in a communications network that provides communicationswith customer premises. A network includes a local exchange carrierwiring. The system includes a NID for providing an interface betweenlocal exchange carrier wiring and customer premises. The system alsoincludes a testing device for testing a portion of the networkterminating at the NID.

In accordance with an additional aspect of the present invention, a testunit is positioned at a NID within a communications network. The NID isin proximity to subscriber premises. The test unit is operative to testat least a portion of the communications network. The test unit includesat least one element for initiating such a test.

In accordance with a further aspect of the present invention, acommunications network includes a NID. Tests are performed with a testunit at the NID to determine whether the communications network isrunning properly and whether any problems exist in the communicationsnetwork.

BRIEF DESCRIPTION OF THE DRAWINGS

An illustrative embodiment of the present invention will be describedbelow relative to the following drawings.

FIG. 1 is a diagram depicting connections between a central switchingoffice and a subscriber's premises.

FIG. 2 is a diagram depicting major components utilized in the operationof a subscriber loop between a central switching office and asubscriber's premises of FIG. 1.

FIG. 3 is a diagram depicting in more detail components employed in anetwork interface device and subscriber premises.

FIG. 4 depicts a test unit in an illustrative embodiment of the presentinvention.

FIG. 5 is a flow chart that provides an overview of the steps performedto complete testing in the illustrative embodiment.

FIG. 6 is a diagram illustrative of a logical component of the testunit.

FIG. 7 is a flow chart illustrating the steps that are performed duringa tone test.

FIG. 8 is a flow chart illustrating the steps that are performed insilencing a phone line by a test unit.

FIG. 9 is a flow chart illustrating the steps that are performed toloop-back a signal by a test unit.

DETAILED DESCRIPTION OF THE INVENTION

The illustrative embodiment of the present invention includes a testunit at a network interface device (NID). The positioning of the testunit at the NID enables testing to determine whether the problem residesat a given subscriber premises or in other portions of thecommunications network. The test unit can perform a number of differenttests to determine whether portions of a communications network areoperating properly. The test unit is remotely activated. It can beactivated, for example, by sending a characteristic radio frequency (RF)signal pattern or a characteristic tone sequence.

FIG. 1 depicts a portion 100 of a communications network between acentral switching office 102 and subscriber premises 104 and 106. Thesubscriber premises 104 and 106 may be a home, an office or otherfacility in which a telephone set is present. Each of the subscriberpremises 104 and 106 includes respective telephone sets 110 and 112.Copper wires 114 and 116 connect the telephone sets 110 and 112 torespective NIDs 124 and 126.

External telephone lines 120 extend from port card 122 at the centralswitching office 102 to the NID 124. Similarly, external telephone lines118 extend from port card 125 to NID 126. Port cards 122 and 125 connecttelephone lines with a central office switch 108. The switch 108 isresponsible for switching calls to appropriate destinations. The switch108 may effect an electrical connection between port card 122 and portcard 125 to establish an end to end telephone connection betweentelephone 110 and telephone 112.

The “subscriber loop” between central switching office 102 and customerpremises 104 is formed by the set of wires and connections that runbetween the port card 122 and the telephone set 110. The “subscriberloop” between the central switching office 102 and the customer premises106 is formed by the set of wires and connections extending from portcard 125 to telephone set 112.

Those skilled in the art will appreciate that the depiction of thecommunication network 100 shown in FIG. 1 is a somewhat simplified viewof a typical communications network. Additional components may becontained within the communications network 100. Moreover, theorganization of the communications network may differ from that depictedin FIG. 1. The depiction in FIG. 1 is intended to be merely illustrativeand not limiting of the present invention.

FIG. 2 depicts components in the central switching office 102 andsubscriber premises (in this case, subscriber premises 104), that areused during normal operation of a telephone subscriber loop. Thesubscriber loop extends from port card 122 at the central switchingoffice 102 through external telephone lines 120 and through NID 124. Thecentral switching office 102 includes a ground 206 and a DC powersource, such as battery 204. The battery 204 may provide a specifiedpotential, such as 48 volts. The battery 204 drives current around thesubscriber loop whenever the circuit (described in more detail below) isclosed by effecting connection between the external telephone lines 120that run through the NID 124. A switch 214 is provided at the subscriberpremises 104. The switch 214 is open whenever a telephone (includingearpiece 210 and mouthpiece 212) is “on hook” (e.g. when the telephonehandset is resting on the cradle). The switch 214 is closed when thetelephone is “off hook” (i.e. when the handset is not resting in thecradle). The closure of the switch 214 effects the closed circuitbetween the battery 204 and the ground 206 at the central switchingoffice 102. As a result, a potential voltage is created that issufficient to drive currents carrying voice (e.g. conversations) anddata signals over the telephone lines 120. When switch 214 is open (i.e.the telephone is on hook), DC potential voltage on the subscriber loopis still there, but no current can flow.

When a call arrives at the central switching office 102 to be connectedto a telephone that includes earpiece 210 and mouthpiece 212 at thesubscriber premises 104, the central switching office takes steps tosignal the need for the subscriber to answer the phone. The signaling isdone by means of a ring generator 202 and a ring detector 208. A switch222 connects the ring generator 202 with port card 122. When switch 222is closed, an alternating current is generated by the ring generator 202and placed onto the telephone line 120. The ring detector 208 recognizesthe alternating current, and generates an audible ring signal at thesubscriber premises 104. When the subscriber hears the telephone ring,the subscriber answers the telephone, resulting in the opening of theswitch 222 and the removal of the alternating current from thesubscriber loop. When the telephone call is completed, switch 214 isopened to remove the voltage potential across the telephone lines 120.Capacitor 216 isolates the ring detector 208 from the DC subscriberloop, so that the ring detector can be activated only by alternatingcurrent.

Against the above-described background, the operation of the test unitmay be better understood. As shown in FIG. 3, the test unit 304 ispositioned in the NID 124 for customer premises 104. For the portion 100of the communications network depicted in FIG. 1, the NID 126 andcustomer premises 106 may have similar configurations to NID 124 andcustomer premises 104, respectively, depicted in FIG. 3. In fact, eachNID within a communications network may optionally include such a testunit.

As shown in FIG. 3, the NID 124 includes an activation signal detector306. This activation signal detector 306 detects a distinct signal foractivating the test unit 304. The distinct signal may be remotelygenerated and sent over the telephone lines 203 to the detector 306. Thedistinct signal may be transmitted from a transmitter 207, shown in FIG.2, at the central switching office 102, which attaches to port card 122as the ring generator 202 via switch 222. In one embodiment, the signalfrom the central switching office 102 is a low-level radio frequencysignal. The preferred signal is the 20-25 kHz range in a band that isnot allocated for commercial broadcasting. Nevertheless, those skilledin the art will appreciate that other bands may be used and thatdifferent distinct signals may be used to practice the presentinvention. The activation signal detector 306 may be implemented as thedetector of the designated radio frequency via a phase locked loop tonedetector. Capacitor 320 isolates the activation signal detector 306 fromthe rest of the subscriber loop. Resistor 322 assures that current doesnot flow into the activation signal detector 306 when the A/C ringsignals are transmitted to the subscriber premises 104.

The NID 124 includes an off hook detector 307. The off hook detector 307detects the increase in DC voltage that occurs when the telephone at thesubscriber premises 104 goes off hook. The off hook detector 306communicates the change to the off hook state to the switch 308. Thoseskilled in the art will appreciate that a number of different types ofelectronic modules may be utilized to implement the off hook detector.There are a number of off-the-shelf commercially available modules forimplementing such functionality.

The NID 124 contains a standard current limiter 310. The current limiter310 is tied to ground and provides protection against surges ofelectricity on the external telephone lines. The current limiter 310 maytake the form of a fuse, an electronic surge protector or a ground shuntthat automatically opens the subscriber loop circuit or runs the currentground when the voltage on the telephone line exceeds a threshold.

Switch 308 controls the behavior of the test unit 304. If the off hookdetector 306 detects an off hook condition, the test unit 304 isdeactivated by opening switch 308. Switch 308 is also controlled byinput from the activation signal detector 306. The activation signaldetector 306 will close the switch (presuming no off hook signal hasbeen detected) when the activation signal is detected. Those skilled inthe art will appreciate that a number of commercially availablecomponents may be utilized to implement switch 308.

The test unit 304 may be implemented using different alternatives. FIG.4 depicts a preferred alternative where the test unit 304 is implementedas a special purpose microcomputer 400. The microcomputer 400 boots upanytime there is a non-negligible voltage between contact points 312 and314 (see FIG. 3). The microcomputer 400 includes a microprocessor 402and storage 404. The storage may include both primary and secondarymemory and may include computer-readable media, such as optical disks,magnetic disks and the like. The storage 404 holds both data 406 andcomputer instructions 408. The data 406 and instructions 408 are used toimplement the various tests performed by the test unit 304.

Those skilled in the art will appreciate that the test unit 304 may bealso be implemented using dedicated electronic circuitry. The test unit304 need not be implemented as a microcomputer. The test unit 304 may beimplemented as servo-activated telephone response module, implementingfunctionality such as that described in co-pending application entitled“Interactive Telephone Response Module” which was filed on Feb. 5, 1998,application Ser. No. 09/019,323, which is explicitly incorporated byreference herein. U.S. patent application Ser. No. 09/019,323 issued onAug. 22, 2000 as U.S. Pat. No. 6,108,404 and is entitled. “Method andSystem for Testing a Connection in a Telephone Network Using InteractiveTelephone Response Module.”Moreover, computing systems other thanmicrocomputers may be utilized for implementing the test unit 304.

FIG. 5 provides a flow chart of the steps that are performed duringtesting. Initially, the test unit 304 is activated by sending anactivation signal from the central switching office 102 toward thesubscriber premises 104 (step 502 in FIG. 5). As was mentioned above,the activation signal is detected by activation signal detector 306. Theactivation signal detector 306 generates an output that closes switch308 so that the test unit 304 becomes active. The test unit 304 isalready running because of the presence of a voltage across end points312 and 314. The test unit 304 then initiates one or more tests toidentify the presence of problems within the telephone network and toidentify the location of the problems within the telephone network (step504 in FIG. 5). When the testing is completed, the test unit 304 may bedeactivated by opening switch 308 (step 506 in FIG. 5).

FIG. 6 depicts the logical components of test unit 304. The test unit304 includes a tone generator 602 for the generation of one or moretones for transmission over the communications network. FIG. 7 is a flowchart illustrating the steps that are performed during a tone test inwhich one or more tones are generated by the tone generator 602.Referring to FIG. 7, initially, a tone is generated at a first test unitwithin the communications network (step 702 in FIG. 7). The tone may,for example, constitute a sinusoidal signal with a predeterminedamplitude and frequency. The tone is then transmitted to a second testunit position within another NID, where the tone is received (step 704in FIG. 7). The second test unit compares the generated tone with thereceived tone to identify the extent of line loss over the line thatconnects the two test units (step 706 in FIG. 7).

The test unit 304 also includes a silencing element 604 as shown in FIG.6. The silencing element 604 is used to silence a portion of thecommunications network. FIG. 8 depicts steps that are preformed in usingthe silencing element 604. A first test unit remains quiescent (step 802in FIG. 8). While the first test unit is silent, a second test unittakes measurements (step 804 in FIG. 8). These measurements may includea measurement of line noise or echo path delay, for example.

The test unit 304 may also include a loop-back element 606. Theloop-back element 606 seeks to return signals in the form in which theywere received. FIG. 9 provides a flow chart of the steps that areperformed using such a loop-back element 606 to perform a test by thetest unit. A first test unit transmits a signal to a second test unit.The signal is received at the second test unit (step 902 in FIG. 9). Thesecond test unit transmits the signal towards the first test unit suchthat the signal is in the same form and at the same level (step 904 inFIG. 9). In other words, the second test unit seeks to echo the signalback towards the first test unit that generated the test signal. Thesignal is received at the first test unit (step 906 in FIG. 9), and thefirst test unit records the time at receipt of the signal so that theroundtrip signal delay may be measured (step 908 in FIG. 9).

The test unit 304 may include a number of other different types ofelements. The logical components 602, 604 and 606 depicted in FIG. 6 areintended to be merely illustrative and not limiting of the presentinvention. For example, the test unit 304 may include components forplaying or for recording and analyzing digitally encoded voice data. Itmay also include capabilies to play or record and analyze digitallyencoded signals representing semantically-encoded waveforms designed totest transmission and receipt of data over acoustic data links ordigital subscriber links in the manner taught in U.S. Pat. No.5,748,876, entitled, “System and Method For Testing Acoustic Modems WithSemantically Encoded Waveforms, issued on May 5, 1998, which isincorporated by reference herein. Furthermore, the test unit 304 mayinclude an acoustic data link with a remote test device for transmittinginstructions and data to the remote test device. This acoustic data linkmay be used to send signals to play and record signals to receiveprocessed data from the remote test device.

While the present invention has been described with reference to anillustrative embodiment thereof, those skilled in the art willappreciate that various changes in form and detail may be made withoutdeparting from the intended scope of the present invention as defined inthe appended claims.

1. In a communication network for providing communications with customerpremises, and said network including local exchange carrier wiring, asystem comprising: a network interface device (NID) for providing aninterface between the local exchange carrier wiring and the customerpremises, said network interface device further includes: a switch; anoff-hook detector to detect use of the communication network at thecustomer premises; and testing device for testing a portion of thenetwork and terminating at the NID, the testing device including asilencing element for silencing the portion of the network, wherein saidoff-hook detector opens said switch to deactivate said testing device.2. The system of claim 1, wherein the testing device includes a remoteactivation module for remote activation of the testing device to performtests.
 3. The system of claim 2, wherein the remote activation moduleincludes a tone detector for detecting at least one characteristic tonefor remote activation of the testing device to perform tests.
 4. Thesystem of claim 2, wherein the remote activation module includes a radiofrequency detector for detecting at least one characteristic radiosignal for remote activation of the testing device.
 5. The system ofclaim 1, wherein the testing device includes a tone generator forgenerating a test tone.
 6. The system of claim 1, wherein the network isa telephone network.
 7. The system of claim 1, wherein the portion ofthe network is quiescent.
 8. The system of claim 1, wherein the testingdevice includes a loop back element for returning signals in a form inwhich the signals are received.
 9. The system of claim 1, wherein thetesting device includes components for playing digitally encoded voicedata.
 10. The system of claim 1, wherein the testing device includescomponents for recording and analyzing digitally encoded voice data.